This invention pertains to the art of jam detection in an electrophotographic printing apparatus and, more particularly, to detection of timing of transport and delivery of sheets in a sheet transport system of a printing apparatus to determine whether slippage of transported sheets has occurred in the sheet transport system.
Electrophotographic printing devices generally include a photoconductive member which is charged to a uniform potential to sensitize the surface of the photoconductive member. The charged photoconductive member is exposed to a light image of an original document to be reproduced which selectively dissipates the charge on the photoconductive member in the areas of the irradiated image and thus forms an electrostatic latent image. The recorded electrostatic latent image on the photoconductive member corresponds to the image of the original document. A developer material including a toner is brought into contact with the photoconductive member and adheres to the photoconductive member in the pattern of the latent image to define a toner image. The toner image is subsequently transferred from the photoconductive member to a sheet of material such as paper, and by heating the sheet, the toner image is fused or fixed on the sheet.
In electrophotographic printing devices, as generally described above, the sheets on which the images are printed are transported to and from the photoconductive member by a sheet transport system which generally includes a system of drive and idler rollers and/or belts which define a sheet transport path. It is important that the sheets move through the sheet transport path with a particular timing which is synchronized to the timing of the imaging system and other systems of the machine. Many known electrophotographic imaging devices employ a registration system which registers the arrival and/or departure of a sheet at different sensing locations within the sheet transport system. The registration system allows jams to be detected when a sheet arrives or departs from a particular sensing location late. The registration system detects a jam when the arrival or departure of the sheet, called a sense event, occurs outside of a predetermined jam period or window. A jam window provides a defined range of acceptable times at which the sense event can occur without a jam being declared.
The occurrence of a sense event outside the jam window which causes a jam to be declared may be due to a variety of different problems within the sheet transport system. For example, slow drift or creeping slippage of the transported sheets within the sheet transport system will cause the sense event to be late. The lateness of the sense event caused by slip may not cause the sense event to occur outside the jam window, however, accumulated slip over time with successive use and wear of the sheet transporting members will cause the sense event to occur outside the jam window and a jam will be declared. With known electrophotographic printing devices, slow slip of sheets is not detected until a jam is declared and the machine is shut down.
Slip of the sheets during sheet transport may be caused by excessive contamination or wear of the rollers and/or belts in the sheet transport system, or by improper adjustment of the sheet transport system. However, the occurrence of slip is generally not detected until a jam is declared and, therefore, the problem which causes the slip is not corrected until the jam has been declared and the machine is shut down.
It would be desirable to be able to pre-warn a service representative of a relatively slow drift or slip of sheets within a sheet transport system causing lateness of sensed events prior to the shutdown of the device due to a jam detection. The service representative receiving the pre-warning could then correct the problem causing the slip (for example on a regular service call) and prevent the downtime caused by a shutdown of the machine at a later time. For example, the operation of the printing apparatus can be interrogated or monitored via a remote interactive communication (RIC) or by interrogating the printing apparatus through a non-volatile memory (NVM). Of course, still other electronic measuring and reporting arrangements are contemplated.
It would also be desirable to be able to determine the portion of the sheet transport path in which the slip is occurring so that the service representative is immediately aware of the location of the problem.